1. Field of the Invention
The invention relates to the field of magnetic write heads for writing a magnetic medium such as a magnetic tape, apparatuses, for example, magnetic tape devices, equipped with such heads, and methods of operation thereof.
2. Description of Related Art
The usable width of a data track in magnetic storage depends on the degree of fidelity with which the ideal transition shape (e.g., a straight line segment) can be imprinted through the volume of the media. Writing of magnetic data is typically achieved by fringing fields arising in the vicinity of the poles of a gapped, “ring”-shaped electromagnet. Because the fringing fields inherently produce finite field distortions at the lateral edges of the poles, the edges of the imprinted transitions are distorted. This results in a “dead” band of finite width at the edge of the written track in which the media is insufficiently uniformly magnetized to contribute to read back signal amplitude.
As track widths tend to decrease in tape products to meet higher areal density requirements, it can be realized that the proportion of the “dead” written track increases. This implies a less efficient use of available media area. This also results in a lower limit of useable media area, unless the width of the “dead” band can be scaled down (at least) at the same rate as the width of the track. Currently, at the level of the technology employed in products, the better known type of distortion is the finite decay length of the write field (and resulting magnetization of the media) in the lateral direction. Often, this effect extends beyond the edges of the write poles, thus impacting the effective track width by over-writing the adjacent track. To date, the acknowledged means of limiting this lateral distortion are to decrease the width of the write gap and to ensure that the edges of the two write poles are well aligned in the cross-track direction. In practice the later can be achieved by the use of “notching” in fabrication, see e.g. U.S. Pat. No. 5,949,625.
As the tape industry moves towards media having smaller magnetic particles with perpendicular orientation, scaled-down tracks, and shorter average bit lengths, other types of distortion become important, notably those that affect the shape of the written-in transition line as opposed to those involving finite abruptness at the lateral edges. One such distortion manifests as a curvature of the transition line immediately track-inwards of the physical edges of the poles (“coma” shape). When this curvature deviates from the ideal straight line, the read back signal amplitude at the track edge is degraded, leading to a loss in signal to noise ratio and hence in a degradation of system performance (as opposed to a reduction in width of the neighboring track).
Moreover, in order to continue scaling tape drive systems to higher areal densities and capacities, it is important to find methods that result in an improved write quality and hence to an improved signal to noise ratio (SNR) of the readback signal. This can be achieved by writing more abrupt transitions, characterized by a small value of the so called transition parameter “a”. This improved SNR can then be used to increase either or both the linear density or the track density.